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Marley Cooling Tower Company Groundwater Treatment System San Joaquin County Inspection Report 'J February 7, 2003 chromium and copper. MCTC has installed and operates a groundwater extraction and treatment system to clean up the polluted groundwater. The discharge of treated groundwater to the Stockton Diverting Canal is regulated by Waste Discharge Requirements (WDR) Order No. 93-221, NPDES Permit No. CA0081787, which was adopted by the Regional Board on 22 October 1993. Under this Order, the Discharger was permitted to extract groundwater and discharge a maximum of 0.94 million gallons per day (mgd) of treated groundwater and storm water runoff to the Stockton Diverting Canal, a water of the United States and a tributary to the Calaveras River. Groundwater Extraction and Treatment System The groundwater treatment system at the plant includes an electrochemical reduction and precipitation unit operating in parallel to an ion exchange treatment system. The system is designed to primarily remove hexavalent chromium from the groundwater. In order to ensure the proper pH of the treated water discharged into the canal, the system is equipped with a pH probe and meter which determines the effluent pH level in the treated water and then activates pH adjustment pumps to adjust the pH in the event the pH level is outside the optimal discharge range of 7.0. Sodium hydroxide (50% by weight) solution is used to adjust the pH level. The system is also designed to completely slut down (with all effluent releases stopped) in the event the pH level measured by the pH probe is outside the range (either too high or too low) of the permitted discharge limits (6.5 to 8.5) in the NPDES permit. Additional in-line meters and interlocks, located in the effluent line after the treatment unit, are designed to shut the system down in the event hexavalent chromium concentrations and Total Dissolved Solids (TDS) in the effluent exceed the effluent limits in the NPDES permit. The groundwater treatment facility has an average monthly flow of 0.72 mgd, and the extraction and treatment systems typically operate continuously 24 hours a day, seven days a week. Receiving Water The Upper Morman Slough drainage course originates from the Calveras River near Bellota. The Upper Morman Slough drainage course then flows west-southwest from Bellota, south of the Calaveras River. The Stockton Diverting Canal, which receives the discharge from the groundwater treatment system, is an engineered drainage which re -connects Upper Mormon Slough to the Calaveras River on the east side of Stockton. From 1 October to 1 April each year, the East Stockton Water District partially blocks off flows from the Calaveras River at its fork with Upper Mormon Slough, diverting some flows during the winter through Upper Mormon Slough and the Stockton Diverting Canal. From 1 April to 1 October each year, flows are split between the Calaveras River and Upper Mormon Slough. A series of check dams are installed along the Calaveras River, Upper Mormon Slough, and the Stockton Diverting Canal to provide irrigation water for adjacent farmers. During this time, there are periods of limited or no flow in the Stockton Diverting Canal. The Basin Plan does not specifically identify beneficial uses for the Stockton Diverting Canal, but the Basin Plan does identify present and potential uses for the Calaveras River, to which the Stockton Diverting Canal is tributary. The Basin Plan identifies the following existing beneficial uses of the Calaveras River, from New Hogan Reservoir to the Delta: municipal and domestic supply (MUN), agricultural supply (AGR) including both irrigation and stock watering; body contact recreation, canoeing and rafting, (REC-1); and other non -body contact recreation (REC-2); warm freshwater habitat (WARM); cold freshwater habitat (COLD), warm and cold migration of aquatic organisms (MIGR), warm and cold habitat spawning, reproduction, and/or early 2 Approved: